Pug mill



Oct. 2, 1951 w. c. WEST PUG MILL l Filed Feb. 14, 1950 2 Sheets-Sheet 1 r I o 1 o o i i o I l T o o o o o 2G 1 Il I o o IN V EN TOR.

Oct. 2, 1951 wA C, WEST 2,570,042

PUG MILL Filed Feb. 14, 195o z sheets-sheet 2 /e l w/ 3- INVENToR.

Y-Wm. /Vesf HTTORNEY.

Patented Oct. l2, 1951 UNITED STATES PATENT OFFF ICE PUG `William C. `West,,Chattanooga Tenn., assignonfto The West Construction-Company, Y(lhattanoogm` Tenn., a corporation of West Virginia Application 'February 14, 1950, SeriarNo144,120(i 2 Claims.

This inventionrelates to. pug mills and more particularlyA to those employed` fory mixing. relatively heavy and/or large aggregates: Withmore or less cementitiousbinding material,the.inven tion having for` its objectto provide afconstruction which is better` adapted-.to handlethis .heavy mixture and whichvis more efcientinfuse than those heretofore proposed.`

With these and other objects in viewitheinvention -resides .intheA novel. details of construction and combinations of parts` as will be disclosed moref fullyr hereinafter and particularly coveredby the claims.`

Referring-to the.accompanyingdrawings, form'- ing a part. of this specification, and in which like parts are designatedlby like numerals,.

Fig. lis a vertical sectionalview takenalong alongitudinal shaft cfa pug mill made in ac^ cordance with this invention;

Fig. 2 is` aver-tical transverse sectional view of the pugV mill shownin Fig. 1,' and:

Fig. 3is an` end elevational view of. saidpug mill.

This pug millislgenerally of avvell-known type as found in this. art, in` that it comprises: two horizontalparallel shafts passing through'amiioing .hopper 4havingirounded bottom portions, ver tical side and endA Walls rising; from said'bottoms, and an lopen top through Awhich the hopper may be charged with the aggregatesl to `be mixed, there also though optionally being, provided heating jackets or chambers associatedrwith the side Walls for insuringiluidity of constituency of certain aggregate material having. abituminous character. The'shafts preferablyare given opposite rotation as by intermeshed drivegears external of the hoppenfthrough the instrumentality of a maindrive gear or pulley mounted on one of the shafts, and a plurality of paddles or stirrers are mounted on each shaft within the hopper. This presentinventionhas to deal with the mounting of said paddles and their relationship one to another.

More specifically and with particular: reference to the drawings, the hopper is generally identified by the numeral 2, theshafts-areindicated at 3 and 4,ithefintermeshed drive gears are shown at 5 and 6 one of `Which may (though not necessarily) constitute the-main drive gear for rotating both shafts, andthe heating jackets are `indicatedat 'l and', see particularly Fig. 3. The bottom of the hopper comprises a substantiallysemicircular Wall portion 9 concentric with the axis of shaft 3, and a similar wall portion |0-concentric Withthe axis of shaftl, With a 2. suitable outlettoriA discharge opening` such:J as Il at"v the lowermost. portion# of cache bottom; Wall, which dischargesare1-1controlled...byu suitable gates suchA as indicated at; l2:` operateds. by a` piston sucln` 'as-l I3 actuated. fromf the power cylinder lil.` The- .openicharging top ofthe hopper` may besuitably` clo'sedlbyeany suitable cover notshown butreadilyunderstood.z Thesshafts are mounted in bearings: such, as l5Y external of the` hopper.

Each shaft VWithincthe;hopper.. has a polygonal (square as. shown) transverse cross-sectional shapeas indicatediat Zur (seeV Fig..2)1,..and upon this. squared` portionofA the` shaft` are mounted the. plurality of paddles or stirrers .extending radially from thel shaft;` It isy an important fea-` ture of this invention that; thesepaddles are arranged inajv seriesrof` setswand areof different radial extent,',the lon-g; paddles:A such as 2| of .a setV alternating. withv shorter paddles: such as a 22 of anv adiacentvsetgreach paddle terminating in anat wear-resistngsplatemsuch.as 23 removably or replaceably mounted :on thepaddle arm,` which plate `has a-.working face .which is angularly` disposed to theradialplanez of rotation rof the paddle so that,` in? the rotationoftheshaft, the ag: gregate material Will be given two directions of movement. one` movement being longitudinally of theshaftandthe otherV movement being circular with respectto .theshaft to the end `that the paddle. assembly will partake ofthe nature ofa screw conveyor. The.. angularity orset of the platesy23 is suchas to move the aggregate material` in a direction fromanendvof thehopper to the centralareathereof,andthetvvo shafts are given rotationalTdii-'ection.such that saidmaterial will be moved circularly from each bottom area of the-.hopper upwardly` at the central por# tion ofthe hopper, seey particularlythe directional arrows in Fig. 2. y

The purpose ofi providingE the long`V paddles 2l is to nsuremovement ofthe aggregate material lying closely. adjacent. to the: inner surface of the hopper, and the-purpose` of. providing the short paddles 22 isl to.r insure movement of the material, lying closelyf adjacent the` shaftandso preventa balling or collection-of.i the material next to the shaft. 'I'he short paddles therefore are* instrumental inV movingn said.V material into the f circular? orl radial rpath. of l the long: paddles:

I The circular orbitrof at=least thelong` paddles of a: shaft;` overlaps.V the-I` circulan orbit ofy the paddles of.- the other shaft `las fclearlyf indicated in Fig. 2,v to insurer-positivermovementpf allof: the material in thehopperl t i The `inmerm'osty'end`-of. each-paddle terminates in a half-bearing 24 adapted to lit the squared portion of its shaft and, when two radially opposed similar paddles are applied to the same shaft, the half-bearings of each are secured together as by the bolts 25. The inner surface of each half-bearing is provided with rectangular (polygonal) notches to fit the corresponding edges or. corners of the vpolygonal portion of the shaft so that the assembly of the paddles on the shaft may be the same as or different from that illustrated in Fig. 2. The polygonal shape of a v shaft may be as desired, but in any event the inner surface of each half-bearing will be complementally formed with respect to the angles, edges or corners of the polygonal shaft.r

Any number of paddles may be mounted longitudinally of a shaft, there being shown the maximum in Fig. l by virtue of the fact that the paddle half-bearings are in sidewisev abutting relation throughout the length of the shaft within thehopper. if a lesser number of paddles is desired than that shown, then spacing collars will be provided between the paddles. The angularsetting of the plate 23 of a paddle may be eected by imparting a twist indicated at 26 to the outer end of the shank of the paddle in the casting thereof, and each plate 23 is secured in place on its .paddle shank as by a squareheaded bolt indicated at 2l, or equivalent means, for ready replacement when unduly worn. rlhe square head of the bolt is countersunk in the plate so as to provide for one of a plurality of selective arrangements (four) of the'plate on the paddle; in other words when the outermost edge such as 2t of a plate becomes unduly worn, lthe bolt may be withdrawn andthe plate turned through 907 to cause another of its edges such as 29 to become the outermost edge. Whereas the foregoingconstitutes a description of the specic construction shown in the drawings, it is to beunderstood. that `variations of said constructions are possible and contemplated,

wherefore the following remarks are presented as a general statement ofV the' basic inventive idea and the purposes and eects accomplished there- Pug mill mixers have beenffor many years, the subject of great `study and many experiments to (a) improve the quality of asphalt paving or other mixtures, (b) reduce the mixing time per batch, to result in'increa'sed production, (c) reduce the power required in operation, and (d) reduce the amount of wear, particularly to expensive manganese vsteel liners. In pug mill mixers the various mixturesrequire different periods of time to obtain a homogeneous mass. Asphalt paving specifications generally require a minimum of from 45 seconds to one minute per batch, or until thoroughly mixed. It has long been knownv that some minerals aggregate and some mixtures cannot be thoroughly mixed in the minimum time period permitted. As the overall capacity of an entire asphalt plant is limited bythe mixer capacity, all plant manufacturers have in recent years built larger mixers, but there is a limit to size as well as other objections.

Applicant discovered some time ago that smaller mixers, having shorter mixing paddles, produced a' more thorough'mixture thanV larger mixers with longvmixing paddles. The conclusion was that in the larger mixer there existed an area or zone `around the mixer shafts wherein the mixing blades on the paddle `extremities'did not thoroughlyagitate and mixtheaggregates with the asphalt cement. The present invention is the solution to this situation and wherein there was installed in a larger mixer both long and short paddles, the short paddles being of further beneiit by replacing spacing collars heretoforeVv used between each pair of paddles. The results from this solution have gone far beyond expectations and were indeed surprising, in that they provided,

(a) An improved quality lof mixture resulting from two mixing zones; one (the outer) zone being that created by the rotation of the longer paddles; and the other zone being created by the rotation of the shorter paddles and disposed within the first or outer zone.

(b) A reduction in the time required to thoroughly mix thel aggregates and asphalt cement by reason of the same two mixing zones.

(c) A reduction in the power required in operation by reason of the additional short paddles, keeping a larger quantity of aggregates somewhat in suspension by the upward throwing action of the short paddles.

(d) A reduction in destructive, effects of abrasion caused by aggregates against the hopper bottom and walls. The same two mixing zones accomplish this by keeping more of the mixture upward and away from the bottom and side walls.

Therefore, the basic and novel principle is seen to reside in the provision of two mixing zones, one within the other, for the ingredients being mixed, Whether they be for asphalt paving or other uses, the paving ingredients being selected herein onlyv as an example. The two mixing zones are represented in Fig. 2, the inner zone being approximately limited by the dotand-dash line 30, and the `outer zone being outf-` wardly limited by the hopper .walls and the dotand-dash line 3i. These two .zones provide a more homogeneousresultant mixture regardless of the specic ingredients, and additionally insure a more positive agitation in the areasad-J jacent the hopper walls and adjacent the shafts.

The setting of the blades, for movement of the material from the ends toward the center of' the hopper, is optional with an alternate setting of the mixing paddles whereby the ma'- terial may be circulated around the periphery of the hopper. Some states require the movement toward the center, others the runaround action. Further, the ingredients for the mix are acted upon as two contiguous portions, one portion circulated by the paddles of shaft 3 rotating in one direction, and the other portion circulated by the paddles of the oppositely rotating shaft ll, both circulating portions being substantially tangent to and merging with each other; and the ingredients in both Zones of each portion'being in contact with each other during circulation by virtue of there being no dividing wall between the zones nor between said portions.

It is obvious that those skilled in the art may vary the details of construction and Varrangements ofv parts without departing from the spirit of this invention wherefore it is desired not to be limited to the exact foregoing disclosure vex cept as may be required by the claims.

What is claimed is:

l. A pug mill or the like comprising a hopper, a pair of horizontally disposed parallel shafts extending longitudinally of said hopper with drive connections for rotating said shafts in opposite directions, and a plurality of paddles extending radially from each shaft for agitating the material within said hopper, said paddles arranged in alternating sets along each shaft, the paddles of one set comprising a pair mounted upon a shaft in diametric radial opposition to each other and of equal length, the paddles of the adjoining set comprising a pair mounted upon the same shaft in diametric radial opposition to each other and of equal length, the pair of paddles of the one set being of a length different from the length of the pair of paddles of the adjoining set, each paddle tted at its outer end with a fiat plate the working face of which is angularly disposed to the radial plane of rotation of the paddle, the paddles of said alternating sets by virtue of their different lengths adapted to create two mixing zones, one zone disposed within the other zone.

2. A pug mill or the like comprising a hopper, a pair of horizontally disposed parallel shafts extending longitudinally of said hopper with drive connections for rotating said shafts in opposite directions, and a plurality of paddles extending radially from each shaft for agitating the material within said hopper, said paddles arranged in alternating sets along each shaft, the paddles of one set comprising a pair mounted upon a shaft in diametric radial opposition to each other and of equal length, the paddles of the adjoining set comprising a pair mounted upon the same shaft in diametric radial opposition to each other and of equal length, the pair of paddles of the one set being of a length different from the length of the pair of paddles of the adjoining set, each paddle fitted at its outer end with a flat plate the working face of which is angularly disposed to the radial plane of rotation of the paddle, the angular disposition of said plates being such as to tend to move the material from each end of the hopper in a direction toward the center thereof, the paddles of said alternating sets by virtue of their different lengths adapted to create two mixing zones, one zone disposed within the other zone.

WILLIAM C. WEST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 228,320 Cornwall et al. June 1, 1880 1,222,584 Barr Apr. 10, 1917 1,483,551 Mosher Feb. 12, 1924 1,519,746 Valerius Dec. 16, 1924 1,555,964 Guedel Oct. 6, 1925 1,987,243 Madsen Jan. 8, 1935 2,187,897 Bollard Jan. 23, 1940 

